Burner for fluid fuels



1970 D. H. DESTY ETAL 3,551,085

BURNER FOR FLUID FUELS Filed Oct. 14. 1968 INVENTORS. I Dams HENRY oEs rY DAVID moumeu WHITEHEAD JOHN LIONEL THOMAS 'WGAN, FINNEGAN, DURHAM a PINE ATTORNEYS United States Patent 3,551,085 BURNER FOR FLUID FUELS Denis Henry Desty, Walton-on-Thames, Surrey, David Montagu Whitehead, Camberley, Surrey, and John Lionel Thomas, Ottershaw, Surrey, England, assignors to The British Petroleum Company Limited, London, England Filed Oct. 14, 1968, Ser. No. 767,339 Claims priority, application Great Britain, Oct. 26, 1967, 48,762/67 Int. Cl. F23d 11/44 U.S. Cl. 431243 7 Claims A burner for fluid fuels comprises a plurality of com bustion air tubes which pass through a. fuel chamber. The tubes connect with the fuel chamber so that, during use, fuel enters the air flowing in the combustion air tubes. Preferably the fuel flow is a curtain close to the wall so that burning takes place close to the wall. Suitable ducts, e.g. annular ducts, achieve this. Conveniently the outlet ends of the combustion air tubes form a heat exchanger.

This invention relates to a burner suitable for use with fluid fuels and particularly to a burner which can conveniently be combined with equipment such as heat exchangers which require a heat source.

According to the invention a burner for fluid fuels comprises a plurality of combustion air tubes which pass through a fuel chamber, the bore of "each combustion air tube being connected with the fuel chamber in such a manner that, in the use of the burner, fuel passes from the fuel chamber into the air flowing in the combustion air tubes. Preferably each combustion air tube has a cylindrical or venturi configuration.

In the preferred embodiment of the invention the connection between the bores of the combustion air tubes and the fuel chamber is such that fuel enters the combustion air tubes in such a manner that it remains adjacent to the walls and burns as a diffusion flame. This can be achieved either by the use of suitably directed ducts or by exploitation of the skin effect.

In the case of suitably directed ducts the bores of the combustion air tubes are connected to the fuel chamber via ducts parallel to the walls of the combustion air tubes, e.g. annular ducts.

The skin effect relates to the tendency of a fluid flowing over a surface to stick to the surface, i.e. the flow will follow a suitably shaped convex surface. Coanda nozzles exploit the skin effect and they are particularly suitable for use in burners according to the invention. A Coanda nozzle comprises a series of facets (arranged so that the internal surface of the combustion air tube becomes the last facet). The facets form a convex surface and during use the fuel flow sticks to this surface so that when it enters the combustion air tube it stays close to the wall.

As well as achieving correct location of the fuel flow a Coanda nozzle also assists aspiration by aerodynamic effects. Venturi configurations for the combustion air tubes are particularly suitable for exploiting these effects.

The burners according to the invention may operate on both gaseous and liquid fuels. In the case of a burner intended for gaseous fuels the connection between the bores of the combustion air tubes and the fuel chamber should provide a resistance to fuel flow which is high in comparison with the resistance of the fuel chamber (i.e. the interstitial space between the tubes). This combination of low resistance followed by high resistance en- Patented Dec. 29, 1970 ice coliglrages uniform flow of fuel into the combustion air tu es.

In the case of a burner which is intended for operation on liquid fuels the high resistance is not so important and the burner is preferably provided with a control device which maintains a working level of liquid in the fuel chamber which is at or close to the connection between the fuel chamber and the bores of the combustion air tubes. With this arrangement the liquid in the fuel chamher is exposed to the heat of combustion and thereby the liquid fuel is vaporised into the combustion air tubes. The control device may take the form of either a constant level or a constant flow device (which is adjustable to provide both low and high thermal outputs).

The invention also includes a combustion device in which the outlet ends of the combustion air tubes of a burner as described above pass through a heat absorbing zone, e.g. heat exchanger, whereby, during the use of the burner, heat derived from the combustion of the fuel is passed into the heat absorbing zone. The combustion of the fuel close to the walls of the tubes (which can be encouraged as described above) facilitates the heat transfer.

A preferred embodiment of a combustion device as described above comprises a fuel chamber situated adjacent to a heat exchanger chamber and a plurality of combustion air tubes which pass through the fuel chamber and the heat exchanger chamber; the bore of each combustion air tube being connected with the interior of the fuel chamber in such a manner that, during the use of the device, fuel passes from the fuel chamber into the bores of the combustion air tubes and the heat produced by the combustion therein is transferred to a heat exchange medium, e.g. water or air, circulated through the heat exchanger chamber.

The invention will now be described by way of example with reference to the drawings accompanying the instant specification of which:

FIG. 1 is a diagrammatic perspective view with part cut-away of a burner according to the invention,

FIG. 2 is a vertical cross-section of a portion of the burner shown in FIG. 1 to an enlarged scale,

FIG. 3 is a horizontal cross-section on the line 33 of FIG. 2, and

FIG. 4 is a vertical cross-section, similar to FIG. 3, of a burner/heat exchanger combination in accordance with the invention.

As can be seen from FIG. 1 the overall appearance of the burner is a rectangular box 10 with a matrix of combustion air tubes 11 which are sealed into an outlet plate 12 and an inlet plate 13.

As can be seen' from FIG. 2 each combustion air tube comprises an upper portion 14 whose lower end fits outside the upper end of a lower portion 15 thereby forming an annular duct 16. The arrangement of the annular ducts and the hexagonal pattern of the combustion air tubes is also illustrated in the horizontal cross-section of FIG. 3.

During use the fuel passes through the interstitial space 17 between the combustion air tubes. It enters the bores of the combustion air tubes via the annular ducts 16 and flows as a curtain of fuel adjacent to the walls of the tubes where combustion takes place as a silent diffusion flame.

In the case of a gas burner the annular ducts 16 collectively provide a high resistance path for the fuel whereas the interstitial space 17 provides a low resistance. This arrangement encourages even flow of fuel into the combustion air tubes.

In the case of a liquid fuel burner the annular ducts 16 have a lower resistance and the burner is fitted with a control device which maintains a level of fuel within the annular ducts. The fuel within the annular ducts is exposed to the radiant heat of combustion which vaporises it into the combustion zone.

The control may be achieved either by an adjustable constant level device or an adjustable constant flow device. In the case of a constant level device the higher the level the greater the heat transfer to the liquid and hence the greater the rate of vaporisation and therefore the greater the heat output. In the use of a constant flow device the level adjusts itself until the rate of vaporisation balances the flow rate. In both cases it is desirable to provide an over-ride to prevent the burner flooding at too high a setting or going out at too low a setting.

FIG. 4 shows a burner as illustrated in FIGS. 1-3 which is combined with a heat exchanger. In this combination the combustion air tubes continue to a top plate 18 instead of terminating at the outlet plate 12. This forms a chamber in which water or air can be circulated through the interstitial space 19.

This arrangement forms a compact and efficient burner/ heat exchanger combination since the heat generated by the combustion within the upper portions 14 of the combustion air tubes is transferred to the water or air circulated through the interstitial space 19.

Preliminary experiments on a prototype laboratory burner/ heat exchanger unit demonstrated that small units are possible.

The overall external dimensions of the prototype were 6 cm. square by 1.5 cm. deep although the combustion air tubes were situated in a centre rectangle 4.2 cm. x 3.5 cm. (i.e. the true burner dimensions were 4.2 cm. x 3.5 cm. x 1.5 cm. deep).

The prototype comprised 25 combustion air tubes 6 mm. in diameter at the outlet end and mm. in diameter at the inlet end. Each tube had an annular inlet (of gap 0.1 mm. and length 3 mm.) whose opening into the tube was about half way along. The interior of the burner was divided into a heat exchanger space and a fuel space of equal volume by a centre partition. The heat exchanger surface area was 28.3 cm.

The prototype was operated on town gas (50% H 30% CH, and rest inert) under a 25 cm. chimney. Burning was by small ring-shaped flames which remained within the combustion air tubes close to the walls.

The following results were obtained:

Fuel gas flow2.0 litres/min. Thermal input-90 Kcals./min. Water flow868 gms./ min. Temperature rise2.5 C.

We claim: 1. -A combustion device which comprises a fuel chamber, a heat exchanger chamber and a plurality of compassage for admixture with combustion air flowing therethrough, whereby, when fuel is fed into the fuel chamber and a heat exchange medium is circulated through the heat exchangerchamber, fuel passes from the fuel chamber into air flowing in said passages of the combustion air tube means and the heat produced by the combustion therein is transferred to the heat exchange medium.

2. A burner for fluid fuels comprising a fuel chamber, a plurality of combustion air tube means through which air will pass positioned within said fuel chamber and extending therethrough in substantially transverse relationship to the'long axis of said chamber, each of said air tube means forming a single passage through said fuel chamber and having fuel inlet means intermediate the ends thereof and within said fuel chamber for passing fuel from said fuel chamber into said passage for admixture with combustion air flowing therethrough.

3. A burner in accordance with claim 2, wherein each of said combustion air tube means includes an upper tube portion having a free end portion and a lower tube portion having a free end portion with the respective free end portions of each being in axially enveloping and laterally spaced relationship with one another and forming an annular inlet passageway therebetween through which fuel willpassfrom the fuel chamber into said single passage for admixture with combustion air flowing therethrough.

4. A burner in accordance with claim 2, wherein said fuel chamber includes opposed plate members spaced from one another in generally parallel relationship, one end of each of said tube means fixed in one of said plate members, with the opposite end of each of said tube means fixed in the other of said plate members.

5. A combustion device in accordance with claim 1, wherein each said combustion air tube means includes an upper tube portion having a free end portion terminating within said fuel chamber and a lower tube portion having a free end portion terminating within said fuel chamber, said free end portions of each of said combustion air tube means being in axially enveloping and laterally spaced relationship with one another and forming an annular fuel inlet passageway within the fuel chamber through which fuel will pass from the fuel chamber into said single passage for admixture with combustion air flowing therethrough.

6. A combustion device in accordance with claim 1, wherein said fuel inlet means forms a fuel inlet duct parallel to said single passage.

7. A burner according to claim 1, in which each combustion air tube means is cylindrical.

References Cited UNITED STATES PATENTS 401,783 4/1889 Kahn 43 l243 2,499,308 2/1950 Griewank 43 l335X 3,047,208 7/1962 Coanda 230 CARROLL B. DORITY, JR., Primary Examiner US. Cl. X.R 43 l203, 335, 354

mg UNITED STATES PA'gfiNp OFFICE CERTIFICATE OF QORRECTION Patent No. 3,551,085 Dated December 29, 1970 Inventor) D. H. Desty, D. H. Whitehead and J. L. Thomas It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Patent, column 3, following line 50 reading:

"Temperature rise 25C.", insert:

--Average Water Temp. 46C

These results give a thermal output to water of 2.2 K

cal/min (i.e. a thermal efficiency of 24% and a heat flux of cals/cm lmin. The thermal output can be increased by using m1 tubes (of the same diameter) and the thermal efficiency can b increased by increasing the length of the tubes (i.e. the heai exchanger surface area).

In a comparative experiment using a similar constructi but with the matrix burner separated from the heat exchanger 1 the combustion zone. a thermal flux of 35 .6 callcm lmin was Signed and sealed this 20th day of Jul; 1 971 (SEAL) Attest:

EDWARD M.FLE'IGHER,JR. WILLIAM E. SCHUYLER, Attesting Officer Commissioner of Pete 

